The present invention relates to an arrangement for controlling switched speech or data communication in a communications exchange.
The invention is particularly useful in electronic telecommunications wherein the exchange speech transmission is handled by a switch block composed of a number of digital switching modules each providing PCM (Pulse Code Modulated) switching in a space-time-space format. Such a switching module is disclosed in British Patent Application No. 2083319A.
The transmission of speech through the switch block is synchronous at a transmission speed of 4 Mb/s, and for intermodule transmission it is necessary that the speech signals are accompanied by bit and frame clock references to allow the receiving module to align the incoming data to its clock reference. Two separate clock signal lines are necessary in the cables use for speech transmission between modules in the switchblock. One line carries a 2 MHz bit clock signal having both positive and negative edges active, and the other line carries the frame start information consisting of a digitally encoded synchronisation pattern in time slot zero.
Accordingly, an aim of the present invention is to provide an arrangement for controlling switched speech or data communication in a communications exchange in an economic and efficient manner by making use of the existing cabling interconnecting switching modules.